U.S. Pat. No. 5,020,562 shows a check valve assembly having resilient valve elements that normally prevent flow through the valve by pressing against a valve seat, but when compressed by a fitting the top of the resilient element the top of the element moves away from the valve seat, thereby permitting fluid to flow therethrough.
U.S. Pat. Nos. 4,683,916 and 4,535,820 show one-way check valves, which use a resilient disk. When these valves are opened it is the outer portion of the disk that is displaced; the disk's central portion is not displaced.